1. Field of the Invention
The present invention relates to developers for positive photoresists.
2. Description of the prior art
Various compounds are disclosed in the prior art as being suitable for use as developers for positive photoresists. Exposure of a positive photoresist to actinic radiation results in a solubility differential between the exposed and unexposed areas such that treatment with an appropriate developer results in removal of the radiation-struck areas and retention of the desired image areas on the support. The criteria for a suitable photoresist developer are speed of development, high selectivity between exposed and unexposed areas, high basicity, and solubility of exposed resin for removal from the film surface.
A typical listing of suitable bases for use as developers appears in U.S. Pat. No. 3,887,450. Included are various primary, secondary, tertiary amines and hydroxyamines; cyclic amines; polyamines; water soluble basic salts of the above; and ammonium hydroxide and tetrasubstituted ammonium hydroxides. In spite of these extensive lists, the most commonly used developers for positive acting photoresists are alkylammonium hydroxides, such as tetramethyl ammonium hydroxide.
U.S. Pat. No. 4,294,911 describes a developing composition comprising a quaternary alkanol ammonium hydroxide developing agent and a stabilizing concentration of a sulfite. The developing composition is stated to be useful for developing light-sensitive compositions containing a quinone diazide. In the preferred embodiment, the quaternary alkanol ammonium hydroxide is methyl triethanol ammonium hydroxide. Such compounds are known in the prior art, but have suffered from the disadvantage of limited shelf-life. Thus, the '911 patent discloses the use of sulfite as a stabilizer.
However, such compositions continue to suffer from several disadvantages. Although the structure provides certain surfactant-like properties, the concomitant foaming would be a disadvantage during processing. Moreover, the relatively higher molecular weight than the simple quaternary ammonium compounds of the prior art, e.g., tetramethyl ammonium hydroxide, tends to increase the development time.
Because of these and other disadvantages, commercially, the simple cuaternary ammonium compounds have continued to be the preferred developing agents. These simple quaternary ammonium developers however, do not exhibit the degree of differential solubilization for exposed and unexposed photoresist that is required to achieve the fine line definition required for advanced microcircuits.
Accordingly, a need exists for compounds which exhibit greater differential solubilization properties towards resins currently used in preparing positive-acting photoresists, and which are more strongly basic and thus better developing agents than the compounds currently used.